A touch pad is usually defined as a touch-sensitive user interface area in an electronic device, which allows a user to input information or a command to the device by pressing the touch sensitive area. The touch pad can be used as a keypad having a designated functionality. For example, a touch pad can be used as an on/off switch and the user can turn the electronic device on or off by pressing the touch sensitive area. The touch pad can have several selectable functions. For example, the touch pad can be used as a keyboard having a plurality of soft-keys of different functions to allow the user to enter or select one function at a time.
In some touch pads, it is required to press the pad surface in order to deform it. In such a touch pad, several layers of material, separated by thin spacers, are used to form a grid of vertical and horizontal rows of electrodes. An electrical current is maintained in the grid of electrodes. When a user presses the pad, the layers are caused to make contact with each other at the pressing point, thereby interrupting the current in the electrode grid. A detection circuit is used to detect the interruption in the current and determine the location of the pressing point on the pad. In other touch pads, mere touching of the pad surface by a finger is sufficient. This latter type of touch pad can be of a resistive-type or capacitive-type. On a resistive-type touch pad, a thin, electrically conductive and resistive layer is coated on the surface of the touch surface area. On a capacitive-type touch pad, a coated layer having a matrix of pixel-like capacitors is provided on the touch sensitive area. When a finger touches the surface, it changes the electrical characteristics of the coated layer. By measuring the resistance or capacitance values at a number of surface points corresponding to the pressing point, the location of the pressing point can be determined. On an inductive-type touch pad, inductive elements are distributed over the touch pad area. A stylus made of an inductive material is used to change the signals transmitted through the inductive elements so that the presence of the style in the proximity of the touch pad can be detected.
Most touch pads can be damaged by having dirt or scratches on the touch sensitive surface. When such a touch pad is implemented on a portable electronic device, such as a mobile phone, the touch pad is usually mechanically protected by a flip, a slide or a cover. When a user wishes to use the touch pad to input information or select a function provided by the touch pad, the flip or cover must be flipped away to expose the touch pad surface to allow the user to touch the touch pad surface. When the electronic device is not in use, the flip or cover is usually flipped back to shield the touch pad surface. Not only does the flip or cover mechanically protect the touch pad surface, it also prevents unintended touching of the touch pad from occurring when the electronic device is put away in a pocket or accidentally dropped or touched. A flip on a mobile phone or similar electronic device usually includes a flip switch or flip mechanism, which can be used to turn on or off the power to the touch pad or the entire electronic device. Thus, when the touch pad is mechanically protected by the flip, the power to the touch pad is also turned off. Thus, even if the touch pad is accidentally touched, which is very unlikely, the touch pad is not functioning.
However, when a touch pad uses a number of optical sensing components, such as light emitters and receivers, to detect the presence of a touching object at the touch pad surface, and the touch pad is designed such that dirt or scratches do not noticeably affect such detection, there is no need to provide a flip or cover on the electronic device to shield the touch pad from mechanical damage when the electronic device is not in use. As the touch pad is exposed to touching regardless of whether the electronic device is in use, accidental touching of the touch pad may have unexpected and sometimes unpleasant consequences.
In some mobile phones, a key lock feature is provided so that the phone can be put in a locked state when the user has no plan to use the phone for a while. When the phone is in a locked state, most of the keypad entries are disabled, but some of the phone functions remain active. For example, the user cannot make a phone call, but the phone can still monitor incoming calls and alert the user to such calls. In some phones, the key lock can be activated by selecting the MENU function followed by the * function to order to put the phone in the locked state. By selecting similar functions, the key lock can be de-activated to “unlock” the phone. If a touch pad device is part of a text/message display of a mobile phone, for example, it is preferred that the display remains functioning even when the phone is in the locked state. This means that the power to the display and, therefore, the touch pad is not turned off. As such, the display can still be used to display text/messages to the user when the phone is in the locked state. Furthermore, a number of selected touch pad functions may still be carried out, but all the non-selected touch pad functions are not carried out after the key lock is activated.
It is advantageous and desirable to provide a method and system for preventing unintended touch pad input resulting from accidental touching, so that the “unavailable” touch pad functions will not be carried out when the phone is the locked state.